The present invention relates generally to the field of air guides used in conjunction with centrifugal fans to provide air power for electric motors. More particularly, the present invention relates to air guide and motor housing structures used with electric motors in appliances, such as vacuum cleaners, and methods of making such structures.
Electric motors are used in many domestic and commercial appliances requiring relatively high suction from a compact electric motor, such as in vacuum cleaners.
Several types of structures are known to redirect a radially outward airstream created by a centrifugal fan so that the redirected airstream flows parallel to the motor longitudinal axis. Typically such a structure, generally designated an "air guide" or "diffuser", is mounted to the motor housing, where it accepts the airflow exiting the centrifugal fan and induces a swirling motion in the airflow as it is redirected into the motor housing.
Torigoe et al. U.S. Pat. No. 4,065,233, Numata et al. U.S. Pat. No. 4,057,370 and Japanese Laid-Open Patent Publication No. 57/1982-30475 provide examples of previously known air guide arrangements, typically involving a centrifugal fan having a central suction intake and a series of spiral shaped impeller vanes that generate a radially outward airflow. This airflow exits into a generally circular chamber, where it is deflected radially off of a casing wall and into the inlet ports of an air guide. The air guide, which comprises a series of fixed spiral vanes, has inlet ports on the side adjacent to the centrifugal fan, and outlet ports on the reverse side. Air entering the air guide through the inlet ports is deflected radially inward to the outlet ports, where it is exits across the motor windings. In such devices, the air guide constitutes a separate element that is aligned with the openings in the motor housing and then affixed to the motor casing using fastening elements.
Japanese Laid-Open Patent Publication No. 1/1989-280700 describes a centrifugal fan, air guide and motor casing arrangement directed to reducing the noise inherent in previously known fan/air guide configurations. The publication notes that the noise resulting from the turbulence created in the airflow as it exits the fan, impinges off the fan casing and passes through the air guide, can be reduced by controlling the gap between the air guide inlet ports and the fan casing.
Similarly, Japanese Laid-Open Patent Publication No. 60/1985-153498 describes a fan/air guide configuration in which the inlet ports of the air guide extend radially outwardly beyond the diameter of the fan. The arrangement described in that publication is an attempt to reduce the noise generated by the airflow passing through the fan/air guide by controlling the ratio of the air guide diameter to the fan diameter, and also by increasing the air guide inlet port area, thereby reducing the quantity of air impinging on the obstructed areas.
A drawback encountered with known air guides is that the exit areas of the air guide must be aligned with the air intake areas of the motor housing. Once so aligned, the air guide is affixed to the motor housing by suitable means, such as screws or rivets. Such structure may have the disadvantage of being difficult to assemble by automated machines, since care must be taken in positioning the air guide so that the air passages of the air guide and motor housing are properly aligned. A further disadvantage of such an arrangement is that the motor housing must provide a surface for accepting the fastening means used to affix the air guide to the motor housing, which in turn reduces the area of the motor housing that can be dedicated as air inlet area. It would therefore be desirable to provide an air guide that reduces the effort needed to align the outlet areas of the air guide with the inlet areas of the motor housing, and that reduces the amount of effort required to fasten the air guide to the motor housing.
Previously known devices typically provide two or more screws or other fastening means to affix the air guide snugly to the motor housing to avoid vibration of the air guide and attendant noise during operation. This mode of attaching the air guide to the motor housing can result in high localized stresses in the air guide where it is attached by the fastening means. As a result, creep deformation of the air guide locally adjacent to the fastening means may result in loosening of the air guide relative to the motor housing, causing vibration and noise during operation. It would therefore be desirable to provide an air guide that can be affixed to the motor housing so as to be resistant to creep-induced deformation and vibration.
The above cited publications show that the noise associated with the turbulence generated in redirecting the airflow exiting the fan into the motor housing can be reduced by controlling the dimensions of the gap between the air guide and the fan casing, and the fan diameter and the air guide diameter. While these parameters permit some noise reduction in the previously known fan/air guide configurations, those designs are limited by the noise created by the constriction of the air flow where it enters the inlet ports of the motor housing. It would therefore be desirable to develop an air guide allowing further noise reduction by reducing the extent of constriction of the airflow as it exits the air guide and enters the motor housing.